Iron-Catalyzed Tertiary Alkylation of Terminal Alkynes with 1,3-Diesters via a Functionalized Alkyl Radical
Direct oxidative C(sp)?H/C(sp3)?H cross-coupling offers an ideal and environmentally benign protocol for C(sp)?C(sp3) bond formations. As such, reactivity and site-selectivity with respect to C(sp3)?H bond cleavage have remained a persistent challenge. Herein is reported a simple method for iron-catalyzed/silver-mediated tertiary alkylation of terminal alkynes with readily available and versatile 1,3-dicarbonyl compounds. The reaction is suitable for an array of substrates and proceeds in a highly selective manner even employing alkanes containing other tertiary, benzylic, and C(sp3)?H bonds alpha to heteroatoms. Elaboration of the products enables the synthesis of a series of versatile building blocks. Control experiments implicate the in situ generation of a tertiary carbon-centered radical species.
Tian, Ming-Qing,Shen, Zhen-Yao,Zhao, Xuefei,Walsh, Patrick J.,Hu, Xu-Hong
p. 9706 - 9711
(2021/03/19)
Diminished helical character in para-substituted cis-transoidal polyphenylacetylenes due to intramolecular cyclization
The cis-transoidal PPA helix undergoes irreversible structural changes related to 6π electrocyclization of 1,3-cis-5-hexatriene sequences in the polymer backbone. The dynamics of the helical conformation is evaluated by optical rotation or circular dichroism (CD) spectra at various temperatures. Helical cis- and trans-poly(alkylacetylenes) exhibit different CD spectra in solutions. In the solution, 1,3-cis-5-hexatriene sequences in PPA and its substituted analogues undergo electrocyclization to form cyclohaxadiene repeat units. The results show that literature data on helical PPA are only qualitative as no complete structural analysis was reported in any previous studies.
Percec, Virgil,Rudick, Jonathan G.,Aqad, Emad
p. 7205 - 7206
(2007/10/03)
Pyrido[1,2-a]pyrazines - Starting materials for regioselective ringtransformation reactions and supramolecular architectures
The easily available pyrido[1,2-a]pyrazines of type 1 are versatile building blocks for ring transformation reactions. With heterocyclic quinones such as quinoline-2,5,8-triones 4a-c, a highly regioselective [4+2]-cycloaddition reaction takes place in the
Müller,Frank,Beckert,G?rls
p. 471 - 478
(2007/10/03)
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